From the recording Pick a Bale of Cotton
I thought this was the proper place to begin, since it's cotton which kept slavery alive and it's slavery that caused the Civil War. The basic contradiction in our country's founding as a land of liberty which allows human bondage finally became impossible to ignore. Those who wished to end the institution and those who did not were beyond reconciliation; the Civil War was the bitter outcome.
It's hard to know when this song was created, but whether it was actually sung in slavery is not as important as the fact that something similar to this call-and-response work song certainly was. Slaves worked from "can to can't," from the time you can see the sun in the morning until you can't see it at night, and if there's a moon and work to do, work they did. Picking cotton is back-breaking work, yet the song makes it sound like lots of fun. It was how enslaved African-Americans dealt with an impossibly bleak situation: they made it bearable through music. Their culture, born in Africa and forged in fire here, can be heard in almost all popular music we listen to today.